Think of Yellowstone as a gigantic pressure cooker, fueled by a massive supervolcano. Water from rain and snowmelt, much of it centuries-old, percolates through cracks in the Earth’s crust until heated by molten rock reservoirs deep below. The water then filters upward, eventually finding release in the thousands of geysers, hot springs, and other hydrothermal wonders.

Eruptions of this supervolcano expel so much material that the crust caves in, creating a craterlike depression called a caldera.

Yellowstone is known as a supervolcano because of the violence and size of its explosions.

The plume of hot rock has been calculated at more than 600 miles deep. But scientists suspect it actually descends as far as 1,800 miles, all the way to what’s known as the Earth’s outer core-mantle boundary.

The reservoirs and plume are superheated, spongelike rock holding pockets of molten material called magma. The reservoirs’ heat, which originates in the plume, is what keeps the area’s geysers boiling.

Ancient rain and snowmelt seep down to just above the volcano’s magma reservoirs, until they are superheated and rise again through the fractures. Volcanic heat and gases help propel steam and water toward the surface, where they escape through hot springs or geysers.